1. Field of the Invention
This invention relates to high pressure duct connections, and more particularly, to an improved method and apparatus for making such connections for air ducts made of sheet metal.
2. Description of the Prior Art
Various types of sealed joints for flanged pipes and ducts have been suggested. Most of these have been difficult to assemble, unnecessarily complex and expensive, and have required separate or extra parts which could be easily lost or had other objectionable characteristics. Many of these disadvantages were overcome in the high pressure duct connection disclosed in U.S. Pat. No. 3,198,561, which patent is assigned to the assignee of the present invention. In aforementioned U.S. Pat. No. 3,198,561, a particular flanged duct connection was described and a C-shaped clamp and wedge arrangement was disclosed for clamping together the duct sections. The present invention is particularly directed to an improved method and apparatus for clamping duct sections, particularly those with flanged arrangements similar to U.S. Pat. No. 3,198,561. The clamp according to the present invention is significantly easier and less expensive to manufacture, requires no more effort to install than the old clamp and further provides a permanent connection, not previously available without having to use nuts and bolts, screws, or rivets.
When two duct sections have been clamped together according to the method of the present invention, the clamp bears somewhat of a resemblance to the type of clamp most commonly known as a "drive-and-slide" clamp. Such a clamp is disclosed for example in U.S. Pat. No. 3,199,901 and British Pat. No. 1,346,366. The clamps disclosed in both of these references rely on the spring tension inherent in the shaped metal forming the clamp. The resulting connection is neither permanent nor positive, since the clamp is subject to bowing out and thereby loosening over time. If the duct is subject to vibrational load stresses, this loosening effect can take place more rapidly.
In contrast to the foregoing, a clamp applied according to the method of the present invention is little more than negligibly susceptible to loosening under vibrational load stress. Further, even should the clamp of the present invention become somewhat loose, its method of application prevents it from slipping and maintains the integrity of the sealed connection.